Umm... whats happened? (I wondered to myself, lying fuzzy in bed at 8 a.m. listening to this stuff on the R4). Did they publish the AR4 a year early with major revisions to the conclusions? No. All this is about (source: BBC) the conference report from the Exeter conference in Feb '05. So (a) its not news; anything in the report (should!) have been said a year ago; and (b) I don't recall the Exeter conf saying much new at the time, either (backed up by the RC post I wrote at the time). And is this a "major report"? Probably not.
The Beeb (check out the video...) picks up on the sea level rise from Greenland: It fears the Greenland ice sheet is likely to melt, leading sea levels to rise by seven metres over 1,000 years. OK, this is fair enough (depending on your scenario it might be more or less than 1000 years, and it might not all be gone for quite a bit thereafter, but its fair enough to be going with... say 5m in 1000 years). But again, its not news, its pretty well in line with the TAR (isn't it? I can't say I've bothered to check). 5m in 1000y is 5mm/yr which is more than the 2-3 mm/yr we have at the moment (and is effectively additional to it) and presumably wouldn't be linear but would come in spurts. Current (and TAR-like) projections for Greenland for the 21st century are much smaller - about 40 mm - which is about right: increasing T increases ppn, but also ablation, so past some (TA-DA!) "tipping point" the SLR contribution from Greenland goes up a lot. But... that pushes the problem a way into the future. Is it reasonable for us to "commit" our descendants to a melting Greenland? (assuming the std.science is correct, and no magic is found, this is what we would be doing).
What else? Above two degrees the risks increase very substantially, involving potentially large numbers of extinctions or even ecosystem collapses. This is onto the bio stuff: could be plausible, I can't comment usefully (I could make it up if you like...). This is linked to the 2oC target the EC has; see my RC post. So, supposing you didn't want to break +2oC (with probability X) you need to limit CO2 to Y; X=60% apparently translates into Y=450 ppmv; since we're currently at 380 my guess is we'll go through 450.
And then it got onto Slashdot which (finally) prompted me to get a slashdot ID and post a comment. See if you can find it. I don't think I'll pursue commenting there... there is just so many comments, so much junk (though some good). This one I quite liked, though others didn't.
[Update: RP has a link to the report pdf itself (I haven't read it yet). Sadly RP also has some dumb comments by Peiser; still, no-one is perfect :-) ]